Best surefire way to do this is to just start over. If you only have one install of IL-2, just uninstall and reload it. Back up your conf.ini and Users folder if you want to save your settings, and your Missions, and Paintschemes folders as necessary if you want to save whatever you had in them. If you plan to do a lot of modding, I recommend keeping a backup of the CLEAN 4.07 version (or whatever the oldest version you installed from is) so you don't have to uninstall/re-install every time. That way you can just make duplicates beforehand and patch each of them to whatever version you need. If you mess up (and trust me, you will at some point) just delete it and make a new copy. CTRL-C and CTRL-V are your friends. I have currently have 8 installs on my drives for different versions and modpacks.

If you have any other questions let us know, and someone will be glad to help you eventually.